Disposable retortable containers are typically formed from either metallic foils, such as aluminum foil, or plastics resins. These containers include a lip portion outwardly extending in a generally horizontal direction along the top opening thereof, providing a sealing region for a closure element.
Membrane closure elements for such retortable containers are also known. Typically, these membranes are heat and/or adhesively bonded to the lip of the container. The seal between the membrane and the container must be capable of withstanding the retort sterilization process, which process occurs in the presence of steam and/or water at temperatures of 250.degree. F. (121.degree. C.) and higher. In order to accomplish this, the membranes in the past have required seal strengths such that peeling of the membrane from the container by hand was impossible.
Attempts have been made to provide a peelable membrane structure. Thus, U.S. Pat. Nos. 3,946,871 and 3,946,872 describe membranes in which the seal between an aluminous metal layer and a plastics resin layer is peeled by breaking of the plastics resin layer. Although it is stated in these patents that such a membrane is retortable, it has been found that the failure rates for these containers during retorting is unacceptably high.
It is thus a primary object of the present invention to provide a peelable membrane structure for containers which can consistently successfully withstand the retort sterilization process.